1. Field of the Invention
This invention relates to a method of securing a lining of plastic material to a substrate having a different coefficient of expansion.
2. Description of the Prior Art
The invention is especially useful in securing sheets of ultra-high molecular weight polyethylene (UHMWPE) to a steel surface, for example, in cladding the hold of a ship. Past attempts to fasten UHMWPE sheeting to a steel or concrete surface have employed various expedients, for example, power actuated fasteners or nuts and bolts. These expedients are exemplified in the brochures entitled "Storage Bin and Hopper Lining with Patented Ultra-High-Molecular Low-Pressure Polyethylene and Modern Fastening Systems", a publication by the Hilti Group and Pennekamp +Huesker KG; "Plastics of Inside Lining" (Bulk Material Storage Bins and Hoppers with High-Molecular Low-Pressure Polyethylene Lining), published by Joseph Robb & Company, Limited and Canadian Hilti Limited; and "ULTRA-CLADD Installation and Fabrication Techniques", put out by Scranton Plastic Laminating, Inc.
The problem with fastening UHMWPE linings to a steel surface, for example, is that the difference in coefficient of expansion between the polyethylene and the steel is such that, when the temperature rises, the sheet material buckles between the fastenings, leaving parts of the lining unsupported and subject to damage by the impact of material being handled. Material also gets between the sheet and the base surface and cannot get out. So, when the sheet cools and contracts it pulls itself off the fastener.
Typical UHMWPE shiphold linings are made up of a number of rectangular sheets placed so that, in one direction, the respective sheets have edges spaced-apart by a narrow gap, and, in the other direction, have overlapping margins. Spaced-apart fastening means hold the sheets to the base surface, each fastening means includes a fastening element permanently connected to the base surface and having a shank extending through an opening in the sheet surrounded by an engagable margin, and head means extending from the shank to hold down the surface of the margin. The sheets may range from 3 feet by 6 feet up to 5 feet by 10 feet. The sheet material may have a thickness within the range from 1/4 of an inch to 2 inches. The UHMWPE may be one of several types. A preferred type has a molecular weight within the range up to 41/2 million and in certain cases the molecular weight may go down as low as 11/2 million or even 1 million. In some cases, hybrid materials may be employed, for example, a mix of polyethylene with silicone to form a composition having an increased coefficient of friction or with elastomers to form a composition having increased impact resistance. The properties of UHMWPE sheeting used for lining steel, concrete, or wood surfaces, are well documented in the technical literature. One thing all these materials have in common is that their coefficient of expansion is considerably greater than the structural material whose surfaces they are used to cover, for example, anywhere from 4 to 5 times that of the usual substrate.